1. Field of the Invention
This invention relates to a video special effect processor for performing video special effect processing on a digital video signal, and more particularly to a video special effect processor for performing video special effect processing on a digital video signal by using depth information.
2. Description of the Prior Art
In preparing television broadcasting programs or video software, etc., a video special effect processor, e.g., as shown in U.S. Pat. No. 4,954,898, is sometimes used. Further, in using video special effect processors of this kind, there are instances in which it is required to synthesize a plurality of images to form a single image. In order to provide such a special effect with synthesis of an image, there is carried out a process such that depth information is added, e.g., to each respective pixel to allow comparison between values of the depth information for pixels corresponding to a plurality of images to be synthesized so that only pixels toward the foreground are displayed and deeper pixels are concealed. In addition, for the purpose Of realizing various special effects, the above-mentioned depth information (which will hereinafter also be called z information) is used.
For example, FIG. 1A shows a display content of a first image, wherein a circle 1 is arranged at a depth position z.sub.1 closest to the screen, and a rectangle 2 is arranged at a depth position z.sub.2 remotest from the screen. On the other hand, FIG. 1B shows a display content of a second image, wherein a triangle 3 is arranged at an intermediate depth position z.sub.3. When such an arrangement of images is assumed, the dimensional relationship of respective depth positions is expressed as follows: EQU z.sub.1 &lt;z.sub.3 &lt;z.sub.2
In order to synthesize these two images FIGS, 1A and 1B to provide an image as indicated by FIG. 1C, a hidden portion process corresponding to the respective depth positions z.sub.1, z.sub.2 and z.sub.3 is required. In actual terms, at the portion where the circle 1 of the image FIG. 1A and the triangle 3 of the image FIG. 1B overlap with each other, the circle 1 is displayed and the triangle 3 is concealed or masked because the relationship z.sub.1 &lt;z.sub.3 holds. On the other hand, and at the portion where the rectangle 2 of the image FIG. 1A and the triangle 3 of the image FIG. 18 overlap with each other, the rectangle 2 is concealed or masked and the triangle 3 is displayed because the relationship z.sub.2 &gt;z.sub.3 holds. It is to be noted that while, for brevity of explanation in FIGS. 1A to 1C, respective shapes 1, 2 and 3 are taken as plane figures in parallel to the screen, i.e., depth positions at all points within the respective shapes are assumed to be equal to each other, depth information is given in practice for each respective pixel of the images.
Meanwhile, although it is possible to transmit the depth information as a parallel digital signal, in such a case, because the depth information is, e.g., several tens of bits per pixel, an exclusive multicore cable is required. Further, an exclusive matrix switcher is required in order to carry out switching between such signals. As a result, the entire system configuration becomes undesirably complicated.